Lectins are well known, multifaceted carbohydrate binding proteins that specifically recognize diverse sugar structures and mediate a variety of biological processes such as cell-cell and host-pathogen interactions, serum glycoprotein turnover and innate immune responses. In 1998, our laboratory solved the first solution structure of a cyanobacterial-derived protein, cyanovirin (CV-N) that exhibited potent HIV- inactivating properties. The structure revealed a novel three-dimensional fold, distinct from any known lectin folds. Extensive biochemical and structural characterizations based on our initial results and primarily from our laboratory led to the categorization of the new structural CVNH family. We previously determined a substantial number of type I CVNH proteins and are now embarking on structure/function studies of type III CVNHs. Similar to our work with CVN, we now have determined the three-dimensional structure of Oscillatoria Agardhii Agglutinin (OAA), another cyanobacterial anti-HIV lectin that shares sequence similarity with eight other proteins, the new OAAH family. No structural, carbohydrate-binding or other functional data were available prior to our recent first structure and no data on any of the family members is available. PUBLIC HEALTH RELEVANCE: Structures, carbohydrate binding and anti-viral activity of CVNH and OAAH family lectins The long-term goal of this proposal is to understand the molecular mechanisms and structural basis of oligosaccharide recognition and the mode of action of HIV-inactivating lectins. We aim to gain a comprehensive molecular understanding of several classes of antiviral lectins and continue with our vigorous program that focuses on elucidating the structural, biochemical, and thermodynamic properties of type III CVNH family members as well as members of the new OAAH family. Results from this work will provide avenues to exploit these lectins in the fight against AIDS.